This invention pertains to new and improved derailer mechanisms and to a specialized cam used in such mechanisms. More specifically it is directed towards derailer mechanisms which are incorporated and used as a part of bicycles.
Because of the various meanings in English of the work "derailer" it is considered necessary to clarify the manner in which this word is used in this specification. This particular word "derailer" was apparently adopted into the English language from French in the mid 1800's to designate a mechanism for removing a wheel from a rail or for removing several wheels from a set or pair of rails. As time has progressed this term "derailer" has been used in English to designate a mechanism for shifting a flexible belt, chain or the like from a first gear or similar member to an adjacent coaxial gear or similar member. The word "derailer" is also utilized to designate the precise structure within such a mechanism which engages and physically re-positions such a belt, chain or the like.
Derailer mechanisms have been commonly employed for many years in connection with bicycles so as to allow the users of such bicycles to vary the particular mechanical advantage associated with the operation of these bicycles. Frequently this is expressed by indicating that a derailer mechanism provides the user of a bicycle with a selection of different gear-ratios sufficient to facilitate the use of the bicycle. It is rather common to describe any bicycle provided with a derailer mechanism for a purpose as indicated as a "derailer" even though the bicycle itself will normally utilize two different derailer mechanisms--one in association with the pedals of the bicycle and the other in association with the rear wheel of the bicycle.
The various prior derailer mechanisms used in connection with bicycles have been constructed a number of different ways. Many of such mechanisms have utilized two different, separate controls, one of which is associated with one of the derailer mechanisms and the other of which is associated with the other of such mechanisms. When used, these two separate different mechanisms had to be manipulated in synchronism with one another so as to avoid any possible interference with the operation of the bicycle. A recognition of the problems associated with this had lead to the development of gear shift mechanisms in which two separate derailer mechanisms or structures are concurrently operated through the use of a single control cable. This use of such a single control cable is highly desirable in that it effectively eliminates the need for coordination in shifting a derailer type bicycle as was required with prior common place structures having two different controls for separately manipulating the two different shifter mechanisms on a bicycle.
In spite of the obvious advantages of derailers employing a single manipulative control as discussed in the preceding it is believed that there is a need for improvement in the field of derailer mechanisms and more specifically in the field of derailer type bicycles equipped with several such mechanisms. Specifically it is considered that there has been a continuing need for derailer mechanisms where are more economical than prior type derailer mechanisms. Further, it is considered that there is a continuing need for derailer mechanisms which are characterized with the ease in which they may be shifted as they are operated. This latter is quite important because the acceptability of a desirable mechanism or structure is frequently dependent upon the "smoothness" with which the mechanism may be shifted and upon the minimization of any possible complications during the operation of a derailer mechanism.